Chapter 1 (Bacterial Cell Ultrastructures) Flashcards by Kathryn Joanne EVANGELISTA

The structure and organization of the cell envelope differs in Gram (+) and Gram (-) bacteria.

It contains components that frequently induce a specific antibody response.

Cell envelope

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Cytoplasmic membrane
Thick peptidoglycan
Variable capsule

Gram (+)

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Cytoplasmic membrane = inner membrane
Single planar sheet of peptidoglycan
Complex layer known = outer membrane
Variable capsule

Gram (-)

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Parts of the cell envelope

Surface adherent structures
Outer membrane
Cell wall
Periplasmic space
Cell membrane

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Appendages of a bacterium

Flagellum
Axial filaments
Microfibrils

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Cytoplasmic structures of a bacterium

Mesosomes
Nucleiod
Ribosomes
Cytoplasmic granules
Endospore
Extrachromosomal factors

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Parts of a bacteria

Cell envelope
Appendages
Cytoplasmic structures

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Slime layer
Capsule
Glycocalyx

Surface adherent structures

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If only a small amount is produced

It is seen as surface layers that are loosely attached to the cell wall and tend to diffuse into the surrounding of the bacterial cell

More easily washed off

Slime Layer

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Example with slime layer

S. lutea

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If polymer forms an additional definite surface layer and is firmly attached to the cell wall

Clearly differentiated from the cell and surrounding

Easily visualized by neg stain (halo)

Fresh isolates of capsulated organisms produce colonies with moist and slimy appearance

Capsule

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Example with capsule

S. pneumoniae
Klebsiella pneumoniae
H. influenzae
B. anthracis
Clostridium perfringens

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If the polymer is seen as a network of fibrils extending from the cell surface,

Seen only be E/M

Glycocalyx

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Example with glycocalyx

Streptococcus mutans

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Among pathogenic bacteria, the presence of capsule is associated with their virulence because it interferes with phagocytosis

Antigenic (Vi antigen) and used in the ID of capsulated organisms

Glycocalyx plays a major role in the adherence of bacteria to cell surfaces

Surface adherent structures

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Found only in Gram (-)

Phospholipid bilayer in which the phospholipids of the outer portion are replaced by lipopolysaccharides (LPS)

Outer Membrane

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Consists of a lipid A and a polysaccharide composed of a core and terminal repeating units

Attached to the OM by noncovalent hydrophobic bonds

lipopolysaccharides (LPS)

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A LPS; component of the outer membrane of Gram neg

Its toxicity is associated with lipid A causing fever and shock

Endotoxin

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Scattered throughout the LPS that form transmembrane diffusion channels that control passage of nutrients and other solutes and provide attachment sites (receptors) for viruses and harmful substances

Porins

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Beneath the OM where, one end is directly attached to the PEPTIDOGLYCAN and the other end to the OM.

Helps anchoring the OM to the underlying peptidoglycan.

Lipoprotein layer

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Outer Membrane parts

Lipopolysaccharides
- endotoxin
- porins
- lipoprotein layer

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Carrier of surface antigens and phage receptors

Act as selective permeability barrier which allows diffusion of molecules with a molecular weight up to about 800

Significance of an Outer Membrane

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Cell wall is also referred to as

Peptidoglycan
Murein
Mucopeptide
Glycopeptide

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Give shape, protection from osmotic lysis and mechanical disruption, and provides necessary support for the propulsion by the flagella

Cell wall

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Cell wall parts

Composed of: - Disaccharide pentapeptide subunits - Teichoic acids - Other auxiliary molecules - Protoplast - Spheroplast

Peptidogylcan sheets made up of alternating sugar compounds [N-acetylglucosamine (NAG) & N-acetylmuramic acid (NAM)] that surrounds the entire cell

Murein sacculus or sack

In gram (+) bacteria that is glycerol or ribitol phosphate polymers in combination w/ various sugars, amino acids and amino sugars

Teichoic acids

They impart properties to the outer surface of gram (+) cells that influence their ability to cause disease

Other auxiliary molecules

The major surface antigens of gram (+) CW

Teichoic acid and CW associated proteins

The disintegration of a cell by rupture of the cell wall or membrane

Lyse/ lysis

It is liberated if stabilized in hypertonic solution of sucrose or salts, a wall-less osmotically sensitive spherical body

Protoplast

The osmotically sensitive body if the cell envelope components are retained

Spheroplast

Found only in Gram (-) Bounded by the internal surface of the OM and the external surface of the CM Consists of a gel-like substance that helps secure nutrients from the environment Contains several enzymes that degrade macromolecules and detoxify environmental solutes that enter through the OM Contains membrane- derived oligosaccharides, various hydrolytic enzymes and proteins that specifically bind sugars, transport materials, amino acids and inorganic ions

Periplasmic space

Found in both Gram (+) and (-) Lipid bilayer heavily laced with various proteins, including a number of enzymes vital to cell metabolism Besides being an additional osmotic barrier, it functions similarity to several of the eukaryotic cell's organelles

Cell membrane

Function of Cell Membrane

1. Transport solutes (in out permeability) 2. House enzymes (synthesis, assembly, secretion) 3. Generation of chemical energy (ATP) 4. Mediation of chromosomal segregation during replication 5. House molecular sensors

Appendages of a bacterium

Flagellum Axial filaments Microfibrils

Filament of uniform length and diameter composed of a protein

Flagellin

External to the cell and connects to the hook at the cell surface

Filament

Attached to the basal body

Hook

Anchored to the plasma membrane and is composed of a rod and 2 or more sets of encircling rings which appear contiguous with the plasma membrane, peptidoglycan and the OM of the cell envelope

Basal body

When flagellated Proteus spp. sometimes swarm in a phenomenon as a thin film of growth in agar media surfaces gave rise to term that indicates a spreading film of growth like breath condensing on a cold glass surface

H antigen (flagellar antigen) - from the German word = Hauch

Employs a chemical (mordant) that precipitates onto the appendage and increases its apparent diameter to resolvable dimensions

Flagellar stain

Messea's classification of bacteria w/ flagella based on location on the bacterial cell:

a. Monotrichous b. Amphitrichous c. Lophotrichous d. Peritrichous e. Atrichous

Flagella: V. cholerae C. jejuni Pseudomonas aeruginosa

Monitrichous

Flagella: Pseudomonas spp

Amphitrichous & Lophotrichous

Flagella: Salmonella typhi Proteus vulgaris

Peritrichous

Flagella: Shigella dysenterjae K. pneumoniae

Atrichous

Significance of flagella

- responsible for rapid motility - antigenically distinct, specific antibody - useful in ID

Motility can be detected by the ff:

1. hanging drop prep examined under LM 2. unstained prep (DWM) examined under DF/ PC 3. spread of bacterial growth as a film over the agar plate - swarming 4. as turbidity spreading through semisolid agar

Some bacteria are able to switch from the production of one antigenic type of flagella to another

Phase variation of flagella

- Found only in spirochetes - Consists of protein fibrils wound spirally around the organism and attached to the 2 poles of the cell - Located just beneath the OM where they function as a flagella-like structure to impart rapid motility to the spirochete (travelling helical wave) - Only seen by EM

Axial filaments

Hairlike structures extending from the cell membrane into the external environment - straighter + thinner + shorter than flagella - observable only by EM

Microfibrils (pili or fimbriae)

Microfibrils is made of protein known as

Pilin

Type of microfibril that is more numerous and found all over the cell surface

Common + Somatic pili

Type of microfibril that is fewer in the number

Sex / conjugal pili

T/F: Both microfibril types may occur either independently or simultaneously on the same cell

True

Common pili are adhesins that help bacteria attach to animal host surfaces and are called _____ when they bind to specific sugars on cell surfaces

Lectins

Serve as conduit for the passage of DNA from donor cell to recipient cell during conjugation

Sex pili

Microfibrils have been implicated in the ______ motion of nonflagellated bacteria on surfaces (surface translocated)

Slow twitching or gliding motion

Usually seen as membrane-associated cytoplasmic sac in Gram (+) cells Contains lamellar tubular or vesicular structures and is often associated with the division septa

Cytoplasmic structures

Parts of the cytoplasmic structures

1. Mesosomes 2. Nucleoid 3. Ribosomes 4. Cytoplasmic granules 5. Endospore 6. Extrachromosomal factors

Septal mesosomes function in DNA replication and cell division Lateral mesosomes function in secretion

Mesosomes

Attached to the CM but more often to the special mesosome rather than directly that houses information for bacterial functions and directs the synthesis of cellular products

Nucleoid

Small roughly spherical cytoplasmic particles Composed of 30% protein + 70% RNA Site of action of many antibiotics that inhibit protein synthesis - Engaged in protein synthesis

Ribosomes

Indicate accumulation of food reserves (storage granules) - used in taxonomy

Cytoplasmic granules

Common types of cytoplasmic granules

Glycogen Polyphosphate granules

Storage form of glucose; major material of enteric bacteria

Glycogen

Storage form of inorganic phosphates that are visible in certain bacteria stained with specific dyes (metachromatic granules, volutin granules) - abundant in M. tuberculosis, C. diptheriae, Yersinia pestis

Polyphosphate granules

Some bacteria are able to form this under adverse physical and chemical conditions, or when nutrients are scarce

Spore (sporulate)

Its formation is a distinguishing feature of the aerobic Genus Bacillus and anaerobic Genus Clostridium - contains large amounts of calcium dipicolinate which confer extreme resistance to adverse environmental conditions

Endospore

The process that restore the actively growing vegetative state

Germination

A highly refractile body within the vegetative bacterial cell

True endospore

They are responsible for heat resistance by making proteins and nucleic acids more resistant to denaturation

Calcium dipicolinate -> dehydration

The core of the spore contains DNA and small cytoplasm w/ stable components of protein synthesis surrounded by several layers that are:

- pore wall - cortex - coat - exosporium

Classification of spores based on location within the cell

- Central - Subterminal - Terminal

Size and location is constant within a species, therefore, it is useful in ID

Taxonomic

Highly resistant to the different methods of sterilization

Clinical

- small, circular, double-stranded pieces of DNA (determine bacterial traits crucial to adaptation, may be antibiotic resistance, tolerance to toxic metals, production of toxins and synthesis of enzymes) - commonly found in the cytoplasm - transferred by conjugation

Extrachromosomal factors

All extrachromosomal pieces of DNA are called

Plasmids

Most plasmids that are transferred by conjugation contains 2 genetic regions

1 - sex pilus 2 - other characteristics of the donor bacteria

Spore is at the long end

Terminal

Spore is at the center

Central

Spore is near end in short

Subterminal

Types of Extrachromosomal factors

a. F b. R c. Colicinogenic d. Virulence plasmids

Provided for the discovery of bacterial sexuality

(F)ertility factor

w/ F factor Male, donors

F+

w/o F factor Female, recipe

F-

Plasmids that contain genes which convert drug-sensitive bacteria to antibiotic resistant cells Drug resistance

(R)esistance factor

Tolerance of microorganisms to antibiotics; may also be brought about by mutation

Drug resistance

Responsible for synthesis of bactericidal proteins (colicins) which are active only against other strains of the same species

(col)icinogenic plasmids

Code for toxin production, like in diphteria toxin production

Virulence plasmids

Chapter 1 (Bacterial Cell Ultrastructures) Flashcards

Part 3 (91 cards)